EP0095431A2 - Process for the preparation of esters by carbonylation of monoolefinic compounds - Google Patents

Abstract

Esters, e.g., alkyl adipates, are facilely prepared by carbonylation among an alcohol, carbon monoxide and a monoolefin, e.g., an alkyl pentenoate, in the presence of a catalytically effective amount of cobalt and a tertiary nitrogen base, and optionally hydrogen, said reaction being carried out in an aromatic hydrocarbon reaction medium bearing from 1 to 3 nuclear substituents, and said substituents comprising cyano or a radical of the formula R-Y- having up to 20 carbon atoms, wherein Y is a direct valence bond, an oxygen atom, a sulfur atom, a carbonyl group or a carbonyloxy group (-CO-O-), with R being bonded to the oxygen of the group -CO-O-, and R is alkyl, aralkyl or or aryl, or a cyano substituted such R-Y- radical, or a radical R-Y- which includes one of the divalent bridges -O-, -CO- or -CO-O- along its skeletal carbon chain, with the proviso that at least one of said substituents is either cyano or a radical R-Y- wherein Y is other than a direct valence bond.

Description

The subject of the present invention is a process for the preparation of esters by carbonylation of monoolefinic compounds, that is to say by reaction of carbon monoxide and an alcohol with compounds containing a single olefinic bond.

A more specific subject of the invention is the preparation of diesters from alkyl pentenates. A particular object of the present invention is the synthesis of alkyl adipates by carbonylation of the alkyl pentenoates.

It is well known, from the "Bulletin of the Chemical Society of Japan, vol. 46, 1973, pages 526 and 527", that a mixture containing alkyl diesters and in particular an alkyl adipate is obtained. , by reacting carbon monoxide and an alcohol on an alkyl pentene-3 oate, under high pressure and at high temperature, in the presence of cobalt carbonyl and of a heterocyclic and aromatic nitrogen base. However, the development on an industrial scale of such a technique, whose interest in principle is not disputed, is largely compromised, not only by the low efficiency of the catalytic system, but also by the significant proportion of pentanoate alkyl formed, although the reaction is carried out in the absence of hydrogen.

It is also well known to these specialists in this field that the presence of small amounts of hydrogen in the reaction medium tends to increase the efficiency of cobalt-based catalysts in the processes for the synthesis of esters by reaction of a alcohol and carbon monoxide on an olefinic compound.

The Applicant has nonetheless noted that in most cases this favorable effect, linked to the presence of small amounts of hydrogen, is accompanied by a negative influence on the selectivity of linear esters, specifically targeted products.

In fact, it is observed that the presence of hydrogen not only increases the proportion of hydrogenation products in the reaction mixture, but also it is capable of decreasing the proportion of linear ester among the esters formed.

This negative effect weighs heavily on the economics of these processes since the valuation of branched esters and hydrogenation products is random, even non-existent. This is particularly the case for branched diesters and alkyl pentanoates produced during the carbonylation of alkyl pentenoates. In fact, these products being destroyed in practice, their formation corresponds, in other words, to an intolerable loss of raw material. Furthermore, hydrogen can be formed in situ from traces of water which may be contained by reagents of technical quality, according to the well-known reaction:

It would be desirable, for obvious economic reasons, to be able to use carbon monoxide of technical quality containing hydrogen, without that happening to the detriment of the selectivity in linear esters, targeted esters. It would also be desirable, for the same reasons, to be able to use reagents containing traces of water, without this leading to a loss of raw material.

It has now been found quite surprisingly that it is possible to selectively prepare linear esters by reaction of an alcohol and carbon monoxide on a compound containing a single olefinic bond, in the presence of cobalt, of a tertiary nitrogen base provided that the reaction is carried out in an aromatic hydrocarbon which comprises from 1 to 3 substituents chosen from the cyano group and the radicals of formula RY- in which Y represents the valence bond, an oxygen atom, a sulfur atom , a carbonyl group or a carbonyloxy group (-CO-O-), the radical R being attached to the oxygen atom of (-CO-O-), R represents an alkyl, aralkyl or aryl radical; said radical, which may optionally include a cyano substituent or a divalent entity -0-; -CO- or -CO-O- inserted in the main carbon chain, contains a maximum of 20 carbon atoms; at least one of the substitutes is chosen from the cyano group and the R-Y radicals, in which Y is different from the valence bond.

• - R₁ et R₂, identiques ou différents, représentent l'hydrogène ou un radical alkyle ayant au maximum 20 atomes de carbone, pouvant être substitué par 1 ou 2 atomes de chlore ou groupes alcoxy renfermant au maximum 4-atomes de carbone,
• - R₁ pouvant en outre représenter un radical -(CH₂)_p-COOH, -(CH₂)_p-COOR₃ ou -(CH₂)_p-CN dans lequel p est un entier au plus égal à 6 pouvant être nul, R₃ représente un radical alkyle comportant au maximum 12 atomes de carbone, un à deux groupements méthylène pouvant en outre comporter un substituant alkyle ayant au maximum 4 atomes de carbone,

According to the present process, carbon monoxide and an alcohol R'-OH are therefore reacted with a compound of formula R ₁ CH = CHR ₂ , in which :

• - R ₁ and R ₂ , identical or different, represent hydrogen or an alkyl radical having at most 20 carbon atoms, which may be substituted by 1 or 2 chlorine atoms or alkoxy groups containing at most 4 carbon atoms,
• - R ₁ can also represent a radical - (CH ₂ ) _p -COOH, - (CH ₂ ) _p -COOR ₃ or - (CH ₂ ) _p -CN in which p is an integer at most equal to 6 which can be zero , R ₃ represents an alkyl radical containing a maximum of 12 carbon atoms, one to two methylene groups which can also comprise an alkyl substituent having a maximum of 4 carbon atoms,

R ₁ and R ₂ can also together form a single bivalent radical - (CH ₂ ) _q -, optionally comprising one or two alkyl substituents having at most 4 carbon atoms, q being an integer between 3 and 6 inclusive,
and R 'is an alkyl radical containing at most 12 carbon atoms optionally substituted by one or two hydroxyl groups, a cycloalkyl radical having from 5 to 7 carbon atoms, an aralkyl radical having from 7 to 12 carbon atoms or a phenyl radical .

The starting materials capable of being carbonylated according to the present process are therefore compounds containing a single internal or terminal olefinic bond; these compounds more specifically contain from 3 to 20 carbon atoms.

By implementing the present process, saturated esters are obtained, that is to say compounds which contain, on the one hand, a carboxylate group (-COOR ') and, on the other hand, a further hydrogen atom. as the starting material. Among these esters predominates the compound whose carboxylate group (-COOR ') is located in the terminal position on the main chain of the starting material.

• R₁CH = CHR₂ dans laquelle R₁ et R₂, identiques ou différents représentent l'hydrogène ou un radical alkyle ayant au maximum 10 atomes de caroone, ou bien forment ensemble un radical unique bivalent -(CH₂)_q- ^q ayant la signification précédente, ledit radical pouvant comporter le cas échéant 1 ou 2 substituants méthyle. A titre d'exemples de tels composés on peut citer le propylène, le butène-1, le outène-2, les hexènes, les octènes et le dooécène-1.

A first category of starting materials more particularly adapted has for formula:

• R ₁ CH = CHR ₂ in which R ₁ and R ₂ , identical or different, represent hydrogen or an alkyl radical having a maximum of 10 carbon atoms, or else together form a single bivalent radical - (CH ₂ ) _q - ^q having the previous meaning, said radical possibly including 1 or 2 methyl substituents if necessary. Examples of such compounds include propylene, butene-1, outene-2, hexenes, octenes and dooecene-1.

• R₁CH = CHR₂ dans laquelle R₁ représente un radical -(CH₂)_p-COOR₃, p et R₃ ayant la signification précédente, un à deux groupements méthylène pouvant comporter un substituant alkyle ayant au maximum 4 atomes de carbone, et R₂ représente l'hydrogène ou un radical alkyle ayant au maximum 4 atomes de carbone.

A second category of starting materials which are more particularly suitable consists of the compounds of formula:

• R ₁ CH = CHR ₂ in which R ₁ represents a radical - (CH ₂ ) _p -COOR ₃ , p and R ₃ having the preceding meaning, one to two methylene groups which may contain an alkyl substituent having at most 4 carbon atoms, and R ₂ represents hydrogen or an alkyl radical having at most 4 carbon atoms.

Among the compounds of this type, the alkyl pentenoates are of particular interest, because they allow access to the alkyl adipates, intermediates of adipic acid.

The present process requires the use of an alcohol of formula R'OH, R 'having the meaning given above.

Examples of alcohols which can be used in the context of the present process include methanol, ethanol, isopropanol, n-propanol, tert-butanol, n-hexanol, cyclohexanol, ethyl- 2 hexanol-1, dodecanol-1, ethylene glycol, hexanediol-1,6, benzyl alcohol, phenylethyl alcohol and phenol.

An alkanol preferably having a maximum of 4 carbon atoms is used; methanol and ethanol are well suited to the implementation of the present process.

The alcohol and the monoolefinic compound can be used in stoichiometric quantities. However, an excess of alcohol is preferably used, in the proportion of 1 to 10, or even better, from 2 to 5 moles of alcohol per mole of monoolefinic compound.

The reaction is carried out in the presence of cobalt. Any source of cobalt capable of reacting with carbon monoxide in the reaction medium to give in situ carbonyl complexes of coDalt can be used in the context of the present process.

Typical sources of cobalt are, for example, finely divided metallic cobalt, inorganic salts such as cobalt nitrate or carbonate, organic salts especially carboxylates. Can also be used cobalt-carbonyls or hydrocarbonyls; dicobaltoctacaroonyle is well suited to the implementation of the present process.

The molar ratio between the monoolefinic compound and the cobalt is generally between 10 and 1000. This ratio is advantageously fixed at a value between 20 and 300.

The process according to the present invention also requires the presence of a tertiary nitrogenous base, the pK of which is between 3 and 10.

The Applicant recommends the use of nitrogen heterocycles formed from 5 to 6 links, which may include one or two substituents chosen from alkyl or alkoxy groups having at most 4 carbon atoms, the hydroxyl group and the halogen atoms, optionally containing 2 or 3 double bonds, and which can moreover, if necessary, be welded to a benzene nucleus, provided that the links adjacent to the nitrogen heteroatom are neither substituted nor common to two rings.

More particularly suitable for the implementation of the present process, the nitrogen heterocycles with 6 links, of pK _a between 4 and 7, in particular pyridine, picoline-4, isoquinoline and lutidine-3,5.

The amount of tertiary nitrogen base used is generally such that the N / Co molar ratio is between 1 and 50. For a good implementation of the invention, the applicant recommends fixing this ratio at a value between 2 and 25 .

One of the essential characteristics of the present process resides in the use, as solvent, of an aromatic hydrocarbon which comprises from 1 to 3 substituents chosen from the cyano group and the radicals of formula RY- in which Y represents the valence bond, an oxygen atom, a sulfur atom, a carbonyl group or a carbonyloxy group (-CO-O-), the radical R being attached to the oxygen atom of (-CO-O-), R represents. an alkyl, aralkyl or aryl radical; said radical which may optionally include a cyano substituent or a divalent entity -O-; -CD-or -CO-O- inserted in the main carbon chain, contains the maximum 20 carbon atoms; at least one of the substituents is chosen from the group cyano and the radicals RY, in which Y is different from the valence bond.

dans laquelle a est un noyau benzénique ou naphtalénique, R₄ représente un groupement cyano ou un radical R-Y, R et Y ayant la signification précédente, Y étant différent du lien valentiel, R₅ et R₆ identiques ou différents, représentent un atome d'hydrogène, un groupement cyano ou un radical R-Y, R et Y ayant la signification précédente, Y pouvant représenter le lien valentiel. De préférence, l'un des radicaux R₅ et R₆ représente l'hydrogène ou un radical R-Y dans lequel Y est le lien valentiel et R est un radical alkyle ayant au maximum 4 atomes de caroone.More specifically, use is made of solvents which can be represented by the formula:

in which a is a benzene or naphthalene ring, R ₄ represents a cyano group or a radical RY, R and Y having the preceding meaning, Y being different from the valential bond, R ₅ and R ₆ identical or different, represent an atom of hydrogen, a cyano group or a radical RY, R and Y having the preceding meaning, Y possibly representing the valential bond. Preferably, one of the radicals R ₅ and R ₆ represents hydrogen or a radical RY in which Y is the valence bond and R is an alkyl radical having at most 4 carbon atoms.

When Y represents an oxygen atom, a sulfur atom, or. a carbonyl group, R is more particularly chosen from alkyl, aralkyl or aryl radicals, comprising at most 10 carbon atoms, and preferably, R is an alkyl radical which contains at most 4 carbon atoms.

When Y represents a carbonyloxy group (-CO-O-) R is identical to the radical R 'of the alcohol used as starting material.

When Y represents the valence bond, R is more particularly chosen from alkyl or aralkyl radicals which have a maximum of 10 carbon atoms and which can comprise a divited entity -0-, -CO- or -CO-0- intercalated in the chain carbonaceous, subject to choosing R identical to R 'when a carbonyloxy entity is inserted in the chain; R can also be a phenyl radical optionally substituted by 1 to 3 alkyl radicals having at most 4 carbon atoms.

Preferably, a is a benzene nucleus. R ₄ is advantageously a radical RY- in which Y represents an oxygen or sulfur atom and R is an alkyl radical which contains at most ₄ carbon atoms or a phenyl radical. R ₅ and R ₆ preferably represent a hydrogen atom.

It is, of course, possible to use mixtures of several of these aromatic compounds.

As examples of solvents suitable for the implementation of the present process, mention may be made of: methoxybenzene (anisole), benzonitrile, methylthiobenzene (thioanisole), ethoxybenzene (phenetole), diphenyl oxide, sulfide diphenyl, diphenyl ether and benzyl sulfide, phenyl and benzyl, _{acetophenone,} propiophenone, n-butylphénylcétone, methyl benzoate, n-butyl, phenyl benzoate, p-tolunitrile, 2-methoxy toluene, 2-ethoxy toluene, p-methylacetophenone, methyl p-toluate, 1,2-dimethoxy benzene (veratrole), 1,3-diethoxy benzene, dimethoxy -1.4 benzene, dimethyl terephthalate, methyl p-methoxybenzoate, methyl p-ethylthiobenzoate, 3,5-dimethyl acetophenone and its isomers, 1,3,5-trimethoxybenzene

Anisole and thioanisole are particularly suitable for the implementation of the present invention.

The amount of solvent which has an influence on the selectivity of the reaction will generally be greater than 20% (by weight) of the initial reaction mixture and, for a good implementation of the present process, it will be between 30 and 60% ( by weight) the above mixture.

According to an advantageous variant of the present process, the reaction is also carried out in the presence of hydrogen. In the context of this variant, hydrogen will represent at least 0.1% (by volume) of carbon monoxide, without however exceeding 3% (by volume). Preferably, the hydrogen content will represent from 0.5 to 2% (by volume) of the carbon monoxide.

Of course, if the hydrogen can be introduced into the reaction medium, in a convenient manner, in the form of a mixture with carbon monoxide, it can also be supplied separately.

The reaction is carried out in the liquid phase at a temperature above 120 ° C, without it being useful to exceed 200 ° C, under a carbon monoxide pressure of at least 50 bars and up to 1000 bars. It is preferred to operate at a temperature of the order of 130 to 180 ° C. and under a carbon monoxide pressure of the order of 100 to 300 bars.

Of course, the optimum pressure and temperature conditions will be all the more severe the less the starting material will be reactive, which occurs, in particular, when the degree of steric protection of the double bond increases.

The carbon monoxide used may contain, in addition to hydrogen, impurities such as carbon dioxide, methane and nitrogen.

As indicated at the beginning of this memo, the method according to the present invention finds a more particularly interesting application in the synthesis of diesters from alkyl pentenoates. In general, an alkyl pentene-3 oate is used, although pentene-2 oates, pentene-4 oates and mixtures of alkyl pentenates can be used. In the context of this application, it turns out to be preferable to choose the alcohol (coreactive) corresponding to the alkyl residue of the starting ester, the alkyl residue advantageously having 4 carbon atoms at most. Good results are obtained starting from one or the other of the following pairs of reagents: methyl pentenoate and methanol, ethyl pentenoate and ethanol.

At the end of the reaction, or when the desired conversion is reached, the linear ester sought is recovered by any suitable means, for example, by distillation or liquid-liquid extraction.

The examples below illustrate the invention without, however, limiting its field or spirit.

PREPARATION OF ALKYL ADIPATE

• Les conventions suivantes sont utilisées ci-après.

EXAMPLES 1 to 27 - Control tests (a) to (i):

• The following conventions are used below.

In the products formed, the compounds resulting from the position isomerization of the olefinic double bond are not included.

The products formed are essentially diesters and alkyl pentanoate, the latter resulting from the hydrogenation of the starting ester.

• - A denotes the activity expressed in moles of products formed per hour and per gram atom of cobalt.
• - X (%) denotes the number of moles of diesters per 100 moles of products formed.
• - Y (%) denotes the number of moles of alkyl adipate per 100 moles of products formed.
• - Z (%) denotes the number of moles of alkyl pentanoate per 100 moles of products formed.

- EXAMPLES 1 to 19 - Control tests (a) to (i):

• A series of tests was carried out according to the following procedure:
• In a 125 ml stainless steel autoclave, purged under argon, methyl pentene-3 oate (P3), methanol, dicobaltoctacarbonyl (DCOC), isoquinoline, and if necessary a solvent are introduced.

• Dans le tableau I(A) les rapports MeOH/P3, P3/Co et N/Co désignent respectivement le rapport molaire du méthanol au pentène-3 oate, le rapport du nombre de moles de pentène-3 oate au nombre d'atomes-grammes de cobalt, et le rapport du nombre de moles d'isoquinoléïne au nombre d'atomes-grammes de cobalt.

The autoclave is then purged by a stream of carbon monoxide containing, where appropriate, hydrogen. The autoclave is then brought to temperature (T), under pressure (P). After a reaction time (designated by t and expressed in hours), at this temperature, the autoclave is cooled and degassed. The reaction mixture is analyzed by gas chromatography. The specific conditions and the results obtained appear respectively in Tables I (A) and I (B) below:

• In Table I (A) the ratios MeOH / P3, P3 / Co and N / Co denote respectively the molar ratio of methanol to pentene-3 oate, the ratio of the number of moles of pentene-3 oate to the number of atoms- grams of cobalt, and the ratio of the number of moles of isoquinolein to the number of gram atoms of cobalt.

In Table I (B), DMMB stands for 3,5-dimethyl methoxybenzene and BM for methyl benzoate.

The control tests (a) to (d) clearly show that in the absence of solvent, the presence of hydrogen results in an increase in the efficiency of the cobalt-based catalyst and in a notable decrease in the selectivity in dimethyl adipate.

Examples 1 to 19 show that the simultaneous presence of a solvent according to the invention and of hydrogen makes it possible to selectively and efficiently obtain dimethyl adipate.

- EXAMPLES 20 to 27:

In the autoclave and according to the procedure described above, a series of tests was carried out on a filler containing 50 mmol of methyl pentene-3 oate (examples 20 to 22, 24 to 26) or pentene-2 methyl oate (P2, examples 23 and 27), 100 mmol of methanol, 1 mmol of dicobaltoctacaroonyl, 8 mmol of isoquinoline and a solvent.

(P3 or P2 / Co = 25; MeOH / P3 or P2 = 2; N / Co = 4)

The specific conditions as well as the results obtained at 160 ° C. under 130 bars are collated in Table II below.

PREPARATION OF DIMETHYL PIMELATE EXAMPLE 28:

• - 44 mmol d'hexène-2 oate de méthyle
• - 100 mmol de méthanol
• - 1,02 mmol de dicobaltoctacarbonyle
• - 7,98 mmol d'isoquinoléine
• - 10,4 g de thioanisole (50 % en poids) .

In the autoclave defined above and according to a procedure similar to that described above, a test is carried out on a load made up of:

• - 44 mmol of 2-methylene hexene
• - 100 mmol of methanol
• - 1.02 mmol of dicobaltoctacarbonyl
• - 7.98 mmol of isoquinoline
• - 10.4 g of thioanisole (50% by weight).

• Le taux de transformation (TT) de l'hexène-2 oate de méthyle en produits de carbonylation et d'hydrogénation (à l'exclusion des produits d'isomérisation de la double liaison) est de : 34,3 %.

In two hours of reaction at 160 ° C., the total pressure at temperature being kept constant and equal to 130 bars by periodic refills of carbon monoxide containing 0.8% (by volume) of hydrogen, the following results are obtained:

• The conversion rate (TT) of 2-hexene-methylate into carbonylation and hydrogenation products (excluding isomerization products of the double bond) is: 34.3%.

• - pimélate de diméthyle : 74 %
• - autres diesters en C₇: 18,5 %
• - hexanoate de méthyle : 7,5 %

The selectivity (RT) of the various products obtained is respectively:

• - dimethyl pimelate: 74%
• - other C ₇ diesters: 18.5%
• - methyl hexanoate: 7.5%

PREPARATION OF METHYL NONANDATE EXAMPLE 29 - control test (j):

• - 50 mmol d'octène-2
• - 100 mmol de méthanol
• - 1 mmol de dicobaltoctacarbonyle
• - 8 mmol d'isoquinoléine

In the autoclave defined above and according to a procedure analogous to that described above, two tests are carried out on a load comprising:

• - 50 mmol of octene-2
• - 100 mmol of methanol
• - 1 mmol of dicobaltoctacarbonyl
• - 8 mmol of isoquinoline

The feed of Example 29 further comprises 10.4 g of thioanisole (50% by weight).

The results obtained respectively in Example 29 and in the control test (j), in two hours of reaction at 160 ° C, under a total pressure at temperature of 130 bars, kept constant by periodic recharges of carbon monoxide containing 0.8% (by volume of hydrogen are indicated in Table III below, in which RT and _T T have a meaning similar to that given in Example 28.

Claims (13)

1. - Process for the preparation of linear esters by reaction of an alcohol and carbon monoxide on a compound containing a single olefinic bond, in the presence of cobalt, of a tertiary nitrogen base and, where appropriate of hydrogen, characterized in that the reaction is carried out in an aromatic hydrocarbon which comprises from 1 to 3 substituents chosen from the cyano group and the radicals of formula RY- in which Y represents the valence bond, an oxygen atom, a sulfur atom, a carbonyl group or a carbonyloxy group (-CO-O-), the radical R being attached to the oxygen atom of (-CO-O-), R represents an alkyl, aralkyl or aryl radical; said radical, which may optionally include a cyano substituent or a divalent entity -0-, -CO- or -CO-0- intercalated in the main carbon chain, contains at most 20 carbon atoms; at least one of the substituents is chosen from the cyano group and the R-Y radicals, in which Y is different from the valential bond. 2.- Method according to claim 1, characterized in that the hyorocarbon has the formula:

in which a is a benzene or napthalenic nucleus, R ₄ represents a cyano group or a radical RY, R and Y having the meaning given in claim 1, Y being different from the valential bond, R ₅ and R ₆ identical or different, represent a hydrogen atom, a cyano group or an RY, R and Y radical having the meaning given in claim 1, Y possibly representing the valential bond. 3. - Method according to claim 2, characterized in that one of these radicals R ₅ and R ₆ represents hydrogen or a radical RY in which Y is the valence bond and R is an alkyl radical having at most 4 atoms of carbon. ₄ . - Method according to claim 2 or 3, characterized in that a is an oenzene nucleus. 5. - Method according to any one of claims 2 to ₄ , characterized in that R ₄ is a radical-RY- in which Y represents an oxygen or sulfur atom and R is an alkyl radical which comprises at most 4 carbon atoms. 6. - Method according to any one of claims 2 to 5, characterized in that R ₅ and R ₆ represent a hydrogen atom. 7. - Method according to any one of the preceding claims, characterized in that the aromatic hydrocarbon represents at least 20% by weight of the initial reaction mixture. 8. - Method according to claim 7, characterized in that the aromatic hydrocarbon represents from 30 to 60% by weight of the initial reaction mixture. 9. - Method according to any one of the preceding claims, characterized in that hydrogen represents at most 3% (by volume) of carbon monoxide. 10. - Method according to any one of the preceding claims, characterized in that the N / Co atomic ratio is between 1 and 50 and, preferably between 2 and 25. 11. - Method according to any one of the preceding claims, characterized in that the reaction temperature is between 120 and 200 ° C, preferably between 130 and 180 ° C. 12. - Method according to any one of the preceding claims, characterized in that the pressure is between 50 and 1000 bars and, preferably, between 100 and 300 bars. 13. - Method according to any one of the preceding claims, characterized in that the compound containing a single olefinic bond is an alkyl penteneate.